Gas generating composition

ABSTRACT

To provide a gas generating composition that has good moldability and inhibits the generation of gas that is harmful to a human body. The gas generating composition contains fuel, an oxidizing agent and a binder selected from sols of inorganic materials.

This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2006-249167 filed in Japan on 14 Sep. 2006, which is incorporated by reference.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to a gas generating composition that can be used in an inflator for an air bag and the like.

2. Description of Related Art

In a gas-generating agent, generally, a binder is used together with fuel and an oxidizing agent, and, because of good moldability and combustion ability, water-soluble organic material-based binders (such as carboxymethyl cellulose, guar gum, starch, polyvinyl alcohol) and organic solvent-based organic binders (such as HTPB: hydroxyl-terminated polybutadiene, GAP: glycidylacidpolymer) are used.

However, in the case where an organic material-based binder is used, there is such problem that a gas harmful to a human body (such as carbon monoxide, nitrogen oxide, ammonia) originating from carbon and nitrogen being constituent elements of the binder is generated (in US-B No. 5,608,183). Further, since the purification action by a secondary chemical reaction of a minute amount of generating gas, which is to be expected normally, is inhibited, the increase in generating harmful gasses is also feared.

Even when a material having no nitrogen is used as an organic material-based binder, due to not only the generation of carbon monoxide originating from carbon but also the increase in oxygen to be consumed for the generation of carbon dioxide caused by the combustion of carbon (Reaction formula I), when considering the reaction in generating gases including the combustion of fuel, it is considered that the purification action caused by the reaction among nitric monoxide, ammonia and oxygen (Reaction formula II) is inhibited, and that the generation of nitric monoxide increases. CH_(x)+(1+(x/4))O₂→CO₂+(x/2)H²O  (I) 2NO+2NH₃+(1/2)O₂→2N₂+3H₂O  (II)

When an inorganic material-based binder is used, there is no such problem as is described above that is caused by the use of an organic material-based binder. However, when compared with the case where an organic material-based binder is used, there is such problem that, in the production by an extrusion-molding method that is frequently used conventionally in the production of gas generating compositions, extrusion moldability is poor (in US-B No. 6,143,102, JP-A No. 5-879, WO-A No. 97/005087 and JP-A No. 11-310490)

SUMMARY OF INVENTION

The present invention relates to a gas generating composition comprising fuel, an oxidizing agent and a binder selected from sols of inorganic materials.

DETAILED DESCRIPTION OF INVENTION

The present invention provides a gas generating composition having improved extrusion moldability, while solving the problem of the case where an organic material-based binder is used as an ingredient of a gas generating composition, and utilizing advantages of an inorganic material-based binder without modification.

The present invention provides the above as means for solving the problem.

It is preferable that the sol of an inorganic material is a sol of a metal oxide. The sol of a metal oxide is preferably one or two or more sols selected from an aluminum oxide sol, a silicon oxide sol, a titanium oxide sol and an antimony oxide sol. The gas generating composition may contain 10 to 70% by mass of fuel, 25 to 85 of the oxidizing agent, and 0.1 to 20% by mass of the binder.

Since the gas generating composition of the present invention contains a binder selected from sols of inorganic materials as the binder, such problem as the generation of a gas that is harmful to a human body as is the case for using an organic binder is resolved, and such problem as poor extrusion moldability as is the case for using a publicly known inorganic binder is also resolved.

EMBODIMENTS OF INVENTION

Fuels used in the present invention may include those used in known gas generating agents, and among those, nitrogen-containing organic compounds are preferred. Examples of the nitrogen-containing organic compound may include one or two or more selected from guanidine nitrate, nitroguanidine, 5-aminotetrazole, ammonium nitrate and melamine.

The oxidizing agents used in the present invention may include those used in known gas generating agents. Among those, examples the oxidizing agent may include one or two or more selected from basic copper nitrate, basic copper carbonate, potassium nitrate, sodium nitrate, strontium nitrate, potassium perchlorate, sodium perchlorate and ammonium perchlorate.

The binder used in the present invention is a sol of an inorganic material. The sol may have water as a dispersion medium or an organic solvent as a dispersion medium. Regarding the sol of an inorganic material, sols of metal oxides are preferred. Examples of the sol of a metal oxide may include one or two or more selected from an aluminum oxide sol, a silicon oxide sol, a titanium oxide sol and an antimony oxide sol.

In the present invention, it is preferable that an organic binder is not included as the binder. However, based on the relationship with an inflator that uses the gas generating composition, or due to the reason of further improving the extrusion moldability, a small amount of an organic binder can be also incorporated. In this case, an organic binder may be incorporated at a ratio of 5% by mass or less relative to the total amount of the solid content of the sol of an inorganic material and the organic binder.

The organic binder may be selected from carboxymethyl cellulose, carboxymethyl cellulose sodium salt, carboxymethyl cellulose potassium salt, carboxymethyl cellulose ammonium salt, cellulose acetate, cellulose acetate butyrate, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethylhydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethylethyl cellulose, microcrystalline cellulose, polyacrylamide, an aminated polyacrylamide, polyacrylhydrazide, acrylamide acrylic acid metal salt copolymer, polyacrylamide.polyacrylic acid ester compound copolymer, polyvinyl alcohol, acrylic rubber, guar gum, starch and silicone.

In the gas generating composition of the present invention, the content fraction of the fuel, the oxidizing agent and the binder is as follows. Regarding the sol of an inorganic material (sol of a metal oxide) being the binder, it is the fraction based on the mass of a solid content that is obtained by removing the dispersion medium.

Regarding the fuel, the fraction is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, further preferably 30 to 50% by mass.

Regarding the oxidizing agent, it is preferably 25 to 85% by mass, more preferably 35 to 70% by mass, further preferably 40 to 60% by mass.

Regarding the binder, it is preferably 0.1 to 25% by mass, more preferably 1 to 20% by mass, further preferably 3 to 15% by mass.

In addition to the fuel, the oxidizing agent and the binder, the gas generating composition of the present invention may incorporate various types of additives contained in known gas generating agents within the range of such volumes that do not injure the purpose of the present invention.

Examples of the additive include one or two or more selected from metal oxides such as copper oxide, iron oxide, zinc oxide, cobalt oxide, manganese oxide, molybdenum oxide, nickel oxide, bismuth oxide, silica and alumina; metal carbonates and basic metal carbonates such as cobalt carbonate, calcium carbonate, a basic zinc carbonate and a basic copper carbonate; complex compounds of metal oxide or hydroxide such as Japanese acid clay, kaolin, talc, bentonite, diatomaceous earth and hydrotalcite; aluminum hydroxide and magnesium hydroxide; metal acid salts such as sodium silicate, mica molybdate, cobalt molybdate and ammonium molybdate, molybdenum disulfide, calcium stearate, silicon nitride and silicon carbide.

The content of an additive is appropriately selected in accordance with the type of the additive, and is preferably about 0.1-20 parts by mass when defining the total amount of the fuel, the oxidizing agent and the binder as 100 parts by mass.

Regarding the method for producing the gas generating composition of the present invention, such a method as mixing the fuel, the oxidizing agent, the binder and an additive if necessary by a kneader to give a mixture and then extrusion-molding the mixture by an extruder can be applied. Incidentally, since the gas generating composition of the present invention uses a sol of an inorganic material containing water or an organic solvent as a dispersion medium, when it is mixed by a kneader, water or an organic solvent may be added according to need.

In the mixing process of the production method of the present invention, when fuel, an oxidizing agent, a binder and one or two or more of additives are used as the components of the gas generating composition, it is also possible to apply a two-step mixing method, in which a part of the components and the binder are mixed, for example, by a kneader to give a primary mixture and then the remaining components are further added and mixed to give the final mixture.

The gas generating composition of the present invention can be molded into a desired shape, and can be formed into a molded article in a single-perforated columnar shape, a perforated columnar shape or a pellet. A single-perforated columnar shape or a perforated columnar shape may have a hole which penetrates in the length direction or a hole which does not penetrate but forms a hollow.

The gas generating composition of the present invention can be applied, for example, to an air bag inflator for the driver side, an air bag inflator for the passenger side, an air bag inflator for side collision, an inflator for inflatable curtains, an inflator for knee bolsters, an inflator for inflatable sheet belts, an inflator for tubular systems, and a gas generator for pretensioners, of various vehicles.

In addition, an inflator that uses the gas generating composition of the present invention can be both of the pyrotechnic type in which gas is supplied only from a gas generating composition, and the hybrid type in which gas is supplied both from a compressed gas such as argon and a gas generating composition.

Further, the gas generating composition of the present invention can be also used as an ignition agent, which is referred to as an enhancing agent (or booster) or the like, for transmitting the energy of a detonator or a squib to a gas generating composition.

EXAMPLES Example and Comparative Examples

Respective components ingredients of Example and Comparative Examples as shown in Table 1 and 16% by mass of water in terms of outer percentage were mixed by a kneader. Next, the obtained mixture (aggregated gas-generating composition) was extrusion-molded by an extruder at a pressure of 80 kg/cm². Samples having been normally extruded were further cut and dried to give gas-generating compositions having an outer diameter of 6.5 mm and a length of 10 mm (in pellet figure with no inner diameter hole).

(1) Evaluation on Extrusion Moldability

The condition of the gas generating composition molded article being extruded upon the extrusion molding according to the above method was observed visually, and the extrusion moldability was determined on the basis of the following evaluation standard.

◯: a level at which the gas generating composition molded article has a sufficient strength to allow it to be extrusion-molded stably (a level at which the extrusion-molded article is not cut over a length of one meter or more to make stable extrusion-molding possible in the above extrusion-molding).

X: a level at which the gas generating composition molded article has an insufficient strength to make stable extrusion-molding impossible (a level at which the extrusion-molded article is cut in a length of less than one meter to make stable extrusion-molding impossible in the above extrusion-molding).

(2) Preparation of a Strand for a Gas Concentration Measurement Test

The gas generating compositions in Example and Comparative Examples obtained in the above (1) were dried at 110° C. for 16 hours. Then, they were crushed, and further filtered twice with a SUS filter having the mesh of 300 μm to adjust the particle diameter. 2.00 g of the mixture having the adjusted particle diameter was charged on the mortar side of a predetermined mold, which was compressed and held at a pressure of 14.7 MPa for 5 seconds with a hydraulic pump from the end face on the pestle side. Then, it was taken out, from which a columnar strand having an outer diameter of 9.55 mm was molded to give a test sample. Incidentally, regarding samples given x in the evaluation of the extrusion moldability, the gas concentration measurement was not conducted.

(3) Measurement of Gas Concentration

The columnar strand being the test sample was placed in a SUS sealed cylinder having an inner volume of one liter. While replacing completely the inside of the cylinder with nitrogen, the pressure was increased up to 7 MPa and stabilized. After that, a predetermined current was applied to a nichrome wire contacted with the end surface of the strand, the energy of which was utilized for ignition and combustion. After waiting for 60 seconds, when the gas in the cylinder became uniform, the stopper-opening portion of a Tedlar bag provided with a predetermined stopper was connected to the gas-discharging portion of the cylinder, and the sample was collected by transferring the combustion gas in the cylinder. The concentration of NO₂, NO, NH₃ and CO in the sample was measured with a gas detector tube (for the detection of NO₂ and NO: No. 1, for the detection of NH₃: No. 3L, for the detection of CO: No. 1L) manufactured by GASTECH CORPORATION). The result is shown in Table 1. The gas concentration in Example 1 is relatively expressed while denoting the gas concentration in Comparative Example 1 by 100%. The result is shown in Table 1. TABLE 1 Example 1 Comparative Ex. 1 Comparative Ex. 2 Gas Fuel Guanidine nitrate (46.2) Guanidine nitrate (40.7) Guanidine nitrate (49.1) generating Oxidizing Basic copper nitrate (42.5) Basic copper nitrate (49.3) Basic copper nitrate (39.9) composition Agent (% by mass) Binder Aluminum oxide sol (11.3) Carboxymethyl cellulose (5) — Additive — Aluminum hydroxide (5) Aluminum oxide powder (11) Extrusion moldability ∘ ∘ x Gas NO₂ 100.00% 100.00% — concentration NO 23.00% 100.00% — (ppm) NH₃ 100.00% 100.00% — CO 82.60% 100.00% — * the content of respective components is shown in % by mass. * the composition ratio of raw materials in Example 1 and Comparative Examples 1, 2 was so determined that the oxygen balance of gas generating compositions became approximately the same value (the oxygen balance here means the amount of oxygen that is excessive or deficient relative to the amount necessary for oxidizing completely the gas generating composition).

As is clear from Table 1, it can be known that the extrusion moldability of Example 1 that used the aluminum oxide sol binder is equivalent to that of Comparative Example 1 that used an organic material-based binder and is clearly excellent when compared with the Comparative Example 2 to which an aluminum oxide powder was added. In other words, it was proved that, even when the sol of a metal oxide of the present invention was used as a binder, the gas generating composition can be produced by an extrusion-molding method in the same way as the case where a conventional organic material-based binder is used.

Regarding the gas concentration, the NO and CO gas concentration in Example 1 was significantly inhibited as compared with Comparative Example 2. In other words, it was known that the present invention has an effect on inhibiting the generation of gas that is harmful to a human body during the combustion of a gas generating composition.

The invention thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A gas generating composition comprising fuel, an oxidizing agent and a binder selected from sols of inorganic materials.
 2. The gas generating composition according to claim 1, wherein the sol of an inorganic material is a sol of a metal oxide.
 3. The gas generating composition according to claim 1 or 2, wherein the sol of a metal oxide is one or two or more sols selected from the group consisting of an aluminum oxide sol, a silicon oxide sol, a titanium oxide sol and an antimony oxide sol.
 4. The gas generating composition according to claim 1 or 2, comprising 10 to 70% by mass of the fuel, 25 to 85% by mass of the oxidizing agent and 0.1 to 20% by mass of the binder. 